Process for bonding rubber to metal



June 21, 1955 PROCESS FOR BONDING RUBBER TO METAL Filed June 19, 1951, T

REACTION PROOucTs OF A (HRESORCINOL WITH ADHERENCE (2) SULPHUR, IN ,ONEOF LAYER THE FOLLOWING FORMS (mm h (a)- SULPHUR, (b) suLPRuRc I-LORIOE,

I (c) THIONYL CHLORIDE.

,f mxz I (I) RUBBE WITH 'RUBBER (2) N-SUBSTITUTED ALDE- HYDIMINES OFGENERAL s p I B FORMULA: R(- N=CH-R')II, I. LAYERA APPLIED TO AOHEsIvEWHERE? I METAL; uLAYER fi NTE 2 R H -L 2.LAYER B APPLIED TO (mm AdhesiveR Is AN. ORGANIC RA IcAL LAYER A; soluhon) Of II\-'VALENCE; "AND 3.METAL WITH LAYERS Aas R HYDROGEN O OR I HEAT TREATED IN PRESENCE OFMONOVALENT RAOIcAL OXYGEN (air) TO FORM AuNrON RESIN L I LAYER (A-PB)CONSTITUTINO A REACTION PRODUCT OF AGE;

4.RUBBER (row) APPLIED TO RESIN LAYER (A-i-B); AND

5.l -IEA T TREATED UNDER PRESSURE TO VULCANIZE RUBBER.

- I INVENTOR S GIOVANNI ANTONIO RusOER &FRANCES CO usso,

G.-A. RUGGERI ETAL I 7 2,711,383

blasting, or by treating the metal in acid baths and then washing anddrying completely.

The ingredients ofthe adherence-layer, which, owing to their affinityfor metals and to their capacity of forming resins by reaction withother ingredients of both solutions, give the bond, according to thepresent invention, may belong to different classes of chemical organiccompounds.

Particularly good results are obtained by employing substances of lowmolecular weight having an affinity for metals, such as phenols, orthiophenols, containing in their molecules more than one substituent,and in the whole, at least two labile hydrogen atoms; the substituentsbeing formed by oxygen, sulphur, halogens, or nitrogen atoms, as singleor linked to one another,'and eventually with hydrogen or carbon atoms.Besides the phenolic hydroxyl .group OH and the thi'ophenolicsulphyc'lril group SH, which are present in the sodefined substances,the substituents may be, for example,

chlorine atoms, bromine atoms, or atomic groups, such as: sulphide -S,disulphide SS, polysulphide Sn, sulphoxide SO--, sulphone SO2,'sulphonium halide ESA (where A indicates an atom of halogen),sulphonium hydroxide =S-OH, oxide O,

primary aminoNHz, secondary aminoNHR (where R is an aryl radical), nitroNOz, or thiocyan --SCN. The labile hydrogen atoms of said phenols andthiophenols, to which the formation of the resin is due by reaction withthe proper ingredients of the same and of the other solution, are thosebelonging to the sylphydril and hydroxyl groups, from which the transferto the aromatic nucleus, or nuclei, occurs at the free positions (orthoand para) to which ultimately the number of the labile hydrogen atomscorresponds.

Besides having the active atoms and atomic groups I above-mentioned,such substances may contain other substituents, which are not eflic'ientfor the purpose of the present invention, as for instance, alkyl,cyc'lo-alkyl, aryl and aralkyl groups.

The following are further examples of substances, suitable for thisinvention, which have a particular affinity for metals and form resinswhen reacting with the other components of the two solutions, ashereinafter indicated: resorcinol, Z-methy'lresorcinol, catechol,pyrogallol, phloroglucinol, 1,3-dimercaptobenzene, mercaptoresorcinols,mercaptohydroquinones, p-bromophenol, 4-chlororesorcinol,2,5dibromohydroqriinone, p-nitrophenol, ethereal anhydroresorcinols,diresorc'inolsulphides, diresorcinoldisulphides,resorcinolpolysulphides, diresorcinolsulphoxides,p,pdihydroxydiphenylsulgihone; chlorides and hydroxydes ofresorcinolsulphonium, p-aminophenol, p hydroxydiphenylamine; and theanalogous derivatives of naphthalene, pure or blended or eventually inform of technical products, or of raw or refined reaction products. Thereaction products of resorcinol, or of the other phenols, with sulphur,with the sulphur chlorides, and with thionyl chloride are to beparticularly remarked.

"Besides the above mentioned products, those phenolic compounds may bepart of the adherence-layer, which have less afiinity for the metals,and, when alone, do not react to form resins, or react-only sluggishlywith the proper ingredients of both solutions, but on the contrary, formresins with the said components when mixed with the phenolic compoundsalready indicated, provided they are present in an amount such as notexceeding the weight ratio of 1:1. These phenolic substances, which willbe called semiactive, in order to distinguish them from the abovementioned, which will be called active, are those containing in theirmolecules only one ,phenolic 'hydroxyl, not connected with any otheractive substituents, and having however in their molecules two or threelabile hydrogen atoms. Examples of semiactive phenolic substances arephenol itself and parametacresol (commercial blend of paraand metacresols).

As antioxidants for the adherence-layer upon its application (that is,before the heat-treatment), other phenolic substances may be added incase this layer contains some products liable to be oxidated in presenceof air, though, also in this case, the addition of an antioxidant is notgenerally required. For this purpose, active and semiactive phenolicsubstances of difierent type, as, for instances, hydroquinone,beta-napththol, monobenzylether of hydroquinone and 2,6-tert.butyl-4-methylphenol, may be employed.

Nitrogenous substances, capable of forming resins when reacting with theabove mentioned substances, and belonging to the series of condensationproducts of ammonia and primary amines with aliphatic, aromatic, andheterocyclic aldehydes, are usually contained in the adherence-layer,even if they are not necessary for the bonding, which however issubstantially improved by them. These basic substances serve also tobring back toward neutrality the pH of the adherence-layer, which mightbe otherwise more or less strongly acid, thus furfuramide, tr'imermethylenethy'lamine, and benzalethyl amine.

The adherence-layer is made by dissolving said components in a commonsolvent, or in a blend of solvents, or by dissolving every component ina particular solvent and mixing the thus obtained solutions. Saidsolvents may be alcohols, as methyl or ethyl alcohol, ketones, asacetone, methylethylketone, halogenated hydrocarbons, as methylenechloride, chloroform, and the like. Water is also employed as a solvent,together with other solvents, it being always a minor component of thetotal mixture.

In order to more easily evaluate the uniformity and the thickness of theadherence-layer during 'its application, said layer may be colored byincorporating mineral or organic pigments in it, and preferably by.addingto it solvent soluble dyes, such as methyl violet, ethyl green,and the like.

The total :ratio by weight between the nitrogenous components and theactive, or semiactive phenolic or thiophenolic substances, may .varywithin .a very wide range; from less than 1:10 to 1:1, and preferablywithin 1:5 and 1:2. The phenolic components to be used as antioxidantsare generally not more than 5% onqthe total weight .of said components;the pigments and the dyeing substances do not exceed,.as a rule,respectively 5% .and 1% on the total weight of the dissolved substances.

The adherence-layer may be applied by -brushing, spraying, dipping, .bymeans of :10llers .or eylindersorlby any other means .capable'of formingon the metalathin continuous layer of uniform thickness. 7

According to its composition, the total dry content of theadherence-layer may .vary from 15% to 20% -or a little more, when .it.is appliedby meansof a paint-brush, and from about 6 to 10%whensprayed. The adhesive solution may be applied .just after thesolvents .of the adherence layer have evaporated.

Thepeculiar components of the adhesive solution, besides the rubbers,that is the ingredients which, when reacting with the peculiarcomponentsof .the adhe ence layer, form the resin-to which the,bond-to-thernetahas well as the bond between the two layers, is due,must be selected according to the composition .of the adherencelayer. Byusing an adherence-layer compounded .as above indicated, ,goodresultsare obtained forthepurposes tofithis invention, .by theemploymentof adhesive solutions containing .Nssubstituted aldehydi'mines, whichcontain .in their molecules two or more azomethynic groups -N==CH, andwhich can be indicated by the general formula R(-N=CH R') 1L; where n isan inte-.

ger number, equal to or higher than 2, R is an organic radical of then-valence and R is one atom of hydrogen, or a monovalentradical; the nRgroups being either equal or different. The said aldehydir'nines maybeemployed as single or mixed, or mixed also with N-substitutedaldearia-tea hydimines having in their molecules only one azomethynicgroup, and eventually with active or semiactive phenolic and/orthiophenolic substances, asidefined in;

the description of the adherence-layer. V a v The N-substitutedaldehydimines. indicated by' the above general formulajhave the chemicalcharacteristic of being double and multiple Schifis bases .and willbe 7called hereafter respectively dialdehydimines and polyaldehydimines andgenerically aldehydimines, thename of monoaldehydimine being givento thesimple Schiffs bases, in which only monovalent radicals are linked to asingle azomethynic group.

R and R (in case R isgnot anhydrogenatomL-may be alkyl, cycloalkyl,aralkyl, or aryl groups (containing one or more simple. or condensednuclei), into which halogenatoms may also be substituted, or elements ofthe oxygen subgroup may be inserted. At least one of the Rs is'howeverpreferablyan olefinic radical,,having a small number of carbon atoms, ora'furyl', or another radical containing one furanic nucleus; and R- ispreferably a bivalent radical, constituted by polymethylenic chainscomprising at least four terms, among which oxygen and sulphur atoms mayalso be inserted.

The di-rand poly-aldehydimine may be easily obtained by condensing(water being formed) primary diamines and polyamines with aldehydes, andprecisely with those containing in their molecules only one-aldehydicgroup, in the ratio of one aldehydic molecule for each primary aminogroup. In order to prepare'the mixed aldehydimines,

that is, those containing R groups differing among them:

two or more difierent aldehydes may be reacted with the same diarnine orpolyamine. i

In preparing the diand polyaldehydimines, thefollowing amino substancesmay be, for instance, employed;

tetramethylenediamine, hexamethylenediamine, di-beta-v aminoethyl ether,di-beta-aminoethyl sulphide, p-phen ylenediamine, m-toluylenediamine,l-chloro-2,4 -diaminobenzene, benzidine, p,p-diaminodiphenylmethane, thenaphthylenediamines, 1,3,5 triaminobenzene, and p,p',p"-triaminotriphenylmethane. In preparing the monoaldehydimines, thefollowing substances may be used: 2-e thy1- hexylamine and aniline. Asaldehydic substances,}the following may be employed: formaldehyde,acetaldehyde, acrolein, crotonaldehyde, benzaldehyde, furfural andfurylacrolein. I 1

As examples of the aldehydiminesthatycan be .em-

ployed for thepurposes of the present-invention, are the following:methylene-furfurylidene-hexamethylenediam ine,di-furfurylidene-hexamethylenediamine, di-furfurylidene-di-beta-aminoethyl sulphide, dimethylene-p-phenyl-'enediamine, di-allylidene-p-phenylenediamine,' difurfuryliwdene-p-phenylenediamine and tri-furfu'rylidene-p,p,p'

triamino-triphenylm'ethane. I 1

Some Schifis bases may polymerize, just after being formed, giving therespective dimers and trimers. These low polymers may also be employedfor the purposes of this invention, but'monomeraldehydirnines;being morereactive, are preferred.

The amount of aldehydimine, or the total amount'of the aldehydimines, tobe incorporated in the adhesive; solution, may vary within a very widerange, as for ex-w ample from 8 to 100% by weight of the rubber, andpreferably'frorn 30 to 80%. The total amounts of the phenolic, and/0rthiophenolic substances, when present, are not as a rule higher than20%, and generally. not over 12% by weight of the rubber. V f

Besides the aldehydimines and the possiblejph'enolic and thiophenolicsubstances required forobtaining the bond, which will be hereafternamed,ffbonding ingredientsj. theadhesive solution may,and'sometimesrnust, contain some. of the usual rubber ingredients, whichmustof course bea'dequate tothe nature ofthefrubber or rubbers presentinthe solution.

'In. case of natural rubber, andof synthetic rubbers formed of polymersor copolymers of'butadiene and its homologues, the solution rna'ycontain Zinc'ioxide and accelerators,- but normallymust not containsulphur; or

otherIvulcanizersj-though, by using somejoi; the afore- 1 mentionedaldehydimin'eaa considerablearnount ofsul- 7,

to the adhesiye solution without a ffecting the bond. T" j i v i W p "f;v Carbonblack, or another reinforcing filler, or a blend of fillers,mustbe present in the adhesive solutions coni" taining the aforesaidsynthetic rubbers, to impart to the 3 formed by themjthe bestfmechanicalphtir' may be added rubber films being properties.

ingredients has to takeplace at a loWerT-templer'ature, the" addition ofantioxidants ,to the. adhesive solutioni's not requir'ed; if Y 'Whenemploying fadhesive solutions based .on" yn';

'theticrubbers which alreadycontain some antioxidants, -.butnevertheless have the tendency toharden and.form.

resins,f'when"subjectel to'a high temperature"heattreatment'in air, sothat the ,desired plasticityandadhesion.

fail, to avoid.thisinconvenience it isgo ften advisable ft add' to theadhesive. solution a pepti'zfing agent,.suchlas i 'betanaphthyl-mercaptam' xylil-mercaptanf 'tirichlorothio- I phenol,o,o-dibenzamide-diphenyldisulphid, in amounts fup toandover 1% byweightoflthe rub'be nj i i 40 Rubber may bepartiallyorentirelysubstituted, already. described f adhesive. vsolutions, by. j reclaimed rubber. I

. The adhesive solutionsrequiredf for bonding syn,

thetic rubber compounds, *base don' polymers or c poly'-' mers of thechlorobutadienes, and vulcanizing'byimeans: Y r of zinc oxide,aretobe'ma'de of the same synthetic .rubfber, together with the usualadhesive ingredients'zand they must not vco ntain zinc oxide. Magnesiumoxide, which acts as anaccelerator for this type of rubbers, j m'ayf beadded, although this. addition isinot strictly require d. J Theadhesivesolution may beprepared by mixingiin V the. rubber, or rubbers, the.bonding agentsas .well asthe otheringredients;ifnecess arily occurring,iand by'dis a blend of solvents, for the rubber or rubbers.

solvlnglthe so-obtainedrubber stockgin a. solvent, or, in

, Some, or thezingredients,including all the manne ones, suchas zincoxide,v and the blacks,.when present,

Inmany-,cases, .th'edifferenttypesof gasoline, well knowninthelrubbenindustry, can beemployed as.sol-.. f

ventsfbut the aromati hydrocarbons and especially .the

mo re, volatile'ones ggas benzene, toluene, xylene), and

v ,be. employed: for synthetic rubbers, c

may lalso fbe incorporatedinj'the rubbers, or infa fractioniof them,andthe so obtained stock dissolvedifjointly with separatelyfrom," theother :cventually require'd rubbers, previouslymilled i'E necessarm-'and' the ingredients not alreadyipresent infthe. stock, in a singlerubber solvent orblend of solvcnts, or:indifferent solvents includingspecial solvents ,forthe nonincorpo'ratedingre- I dients, the separate,solutions gbeing in thelast ca'seiaci curately mixed. .I,

sometimes "also chloroforrn, are preferred, because they generallydissolve' als of the aldehydimin esq' If necessary, v specialsoly ents"as methylethylketonei andjbutyl i acetate;:or -their blends, withsomeotherfsolvents, may' phenolic f 7 or thiophenolic substances are tobe added in solution, acetone may be employed as a solvent for them, insuch a quantity not to cause the rubber or rubbers to precipitate; thepresence of rubber being generally sufficient to keep in dispersion allingredients. The use of alcohols must be avoided.

The solvents or the blends of solvents mentioned above have theadvantage of not dissolving considerably the most important of theingredients of the adherencelayer; the inconvenience of displacing themwhile applying the adhesive solution being thus avoided.

The adhesive solution may be applied according to any process mentionedin describing the application of the adherence-layer. According to thecomposition of the adhesive solution, its total dry solid content mayvary 1.

from 6 to 17% when it is applied by means of a paintbrush, and fromapproximately 3 to 6% when it is applied by spraying.

For a same application, the amounts of solids deposited on a givensurface, from the adherence-layer and the adhesive solution, may varywithin a considerably wide range. Nevertheless they are not quiteindependeat, but must be proportional. Their ratio may vary according tothe respective compositions; for the most usual compositions, said ratioranging from 1:3 to 1:7.

The soluticned metal parts can be heat-treated as soon as the solventsof the adhesive solution are evaporated, that is, about half an hourafter the application of the solution; or also a shorter time after,especially if the film formed by the said solution is very thin. Ifnecessary, the solutioned metal parts may also be heat-treated somehours after the adhesive solution has been applied.

The heat treatment may be carried out under superatmospheric pressure,although normal atmospheric pressure is preferred, in an oven, preheatedat the desired temperature and containing air, or air enriched withoxygen, or ozonized air, or a mixture of gases containing not less than20% by volume of oxygen and so compounded that its other components donot exert any chemical action either on the metal or on the componentsof the layers formed from the adherence-layer and the adhesive solution.The said treatment can also be carried out under reduced pressure, butthis is not of any practical utility.

In the oven the air, or the other oxygen-containing gaseons mixture,must have a relative humidity (measured at room temperature) not higherthan 80% and preferably about 50%.

Temperature and time of the heat-treatment may vary according to thecompositions of the adherence-layer and the adhesive solution. For givencompositions, the time is dependent on the temperature; that is, thesame result may be obtained by a short heat-treatment at a hightemperature, or by a longer heat-treatment at a lower temperature. For agiven temperature, the time may however vary within a considerably widerange. The limits within which the heat-treatment time may vary, at agiven temperature, increase as the temperature is lowered.

For adherence-layers and adhesive solutions compounded with the abovementioned bonding ingredients, the temperature may vary from less than110 C. to over 170 C., and at 140 C. a two hours treatment is generallysufiicient.

The resinification time for a given temperature being known, the timerequired for a different temperature may be approximately calculated,within acceptable limits, by doubling it or by dividing it by two, forevery decrease or increase of about 8 C. in temperature. It is preferredthat, during the heat-treatment, the air or the other oxygen-containinggaseous mixture be circulated inside the oven, thus facilitating theraising in temperature of the solutioned metal parts, and providing amore uniform distribution of the temperatures inside the oven.

Time and temperature of the vulcanizing heat-treatmea 9 h as e bcompared of h nata Parts tr eted as above described, on which the'vulcanizable 'rnbb compound has been applied, must be suchas to assurea rubber compound at the beginning of the heat-treatment;

and its thickness being so little, that'the time required for saidmigration is practically negligible. vulcanization times of 20 minute sat 143 C. or oil hour at 127 C. and also shorter times at highertemperatures, are generally suflicient. V i I '1 As already mentioned,one of the greatest advantages of our novel bonding process, comparedwith thois e involving brass-plating and others'already knownfis thefact that there are practically almost no'limi'ts to the composition ofthe vulcanizable rubber compound'to be bonded. Said rubber compoundmaycontain any adcelerator and any activating agent for said accelerators,as for instance stearic acid (also in a high percentage: 3%- or more byweight of the rubber), "amendment any type and plasticizers even inlarge amounts, and reclaimed rubber of any kind. Sulphur curing rubbercom pounds and rubber compounds curing with other sulphuratedvulcanizing agents, such as tetramethylthiouram disulphide, in properamounts, give equally good results, said compounds being based either onnatural rubber, or on synthetic rubbers consisting of polymers orcopolymers of butadiene or its homologues.

Rubber compounds, showing (after vulcanization) hardnesses ranging from32 to Shore A and over, bond likewise satisfactorily. The softer rubbercompounds, deforming under load to a greater extentpare subjected underload to such aconcentration of stresses that they break ofi as a ruleunder total loads which are less than those recorded forthe harderrubber compounds, wherein the rubber rupture occurs more easilyf Thisinconvenience may be avoided by applying to the solutioned heat-treatedmetal parts one or more layers of a solution, or a thin calendered sheetof a harder rubber compound having the same vulcanization time as thesoft rubber compounds to be bonded, and containing the same acceleratorsand vulcanizing ingredients; and thereafter assembling to the metalparts the rubber compound to be bonded and vulcanizing the compositearticle.

One of the advantages of the process of this invention is that a singleadherence-layer permits satisfactory bonds, to be obtained withindustrial metals and metal alloys, having very different chemical andphysical characteristics, such as: ingot iron, carbon steel, stainlesssteel (containing 18% ofinickeland 8 of chrome),.copper, aluminum, zinc,lead, tin, brass, bronze and even nickel andchronie. More exactly, ourimproved bonding process is applicable to .allt he metals which formwater-insoluble hydroxides, but it .is not applicable to the alkali andalkaline earth metals (e. g. sodium and calcium), which can not be usedin the manufacture of rubber to-metal bonded articles.

.On the other hand, by .using dilferent adhcrence-layersin connectionwithspecialmetals, orgroups of metals, more satisfactoryresults maybeobtained.

By using a given adherence-layer together with a single adhesive.solution based on natural rubber, satisfactorybonds may ,beobtainedeither with the vulcanizable natural rubber compounds or with thosebased on synthetic rubbers comprising copolymers of ,butadiene andstyrene ,(Buna S, GR-S) alone, or in mixture .with natural rubber,,orwith those based on .thioplasts (Thiokol A, Thiokol D, Thiokol F),especially if these latter-contain even small amounts of natural rubber.Satisfactory bonds are also obtained with the said styrene-containingsynthetic rubbers, by using adhesive solutions ,based on the samesynthetic rubbers. This latter method must necessarily be used to bondthe other synthetiorubberconsistingof copolymers of. butadiene andacrylonitrile (Perbunan, I-lycar OR, Polysar N), or of polymers orcopolymers of the chl'orobutadienes (Neoprene GN, Neoprene GNA), orofcopolymers of'isobutylene and] small amounts of butadiene or isoprene.(butyl rubbers). The resistance of the bond tothe swelling" action ofthe solvents and plasticizers is generally similar to, or greater than,that shown by the vulcanized-rubber com? pounds assembled to the metals,provided -that the adhesive solution has been prepared with thesamerubber, or mixture of rubbers, present in the compound; the resinformed by the adhesive ingredients being, per-se, insoluble in thevarious solvents orplasticiZers. v The heat-resistance of the bond isvery satisfactory, In the mechanical tests carried out at temperatureabove: the room temperature, for instance at 100 C., the rupturegenerally occurs in the rubberinstead of in the bond between the rubberand the metalpartsythe mechanicalresistance of the rubber decreasingmore rapidly than, that of the bond itself. The same result isobtainedwhen the tests are carried out with oven-aged specimens. f

Another very remarkableadvantage of. this processis metrical withrespect to'the centre of the specimen; The; cylindrical surfacespoftthisring: are respectively bonded testing machine. The diametjers and; the.highnesseswof V p the; cylindrical? surfaces" are proportionedsofastohave, H inthe rubbenpart of the specimen under-test ashean {loadwhich is equalin theinternalandinthe external cylindrical layersbondedto themetal parts. The; cylindr s rme i urf l e b vb di d a .s q'th :aThe;

hydraulic steam-heated press.

is V

of 2 0% 'i b 'ha r .a w yssu fi ient detachment;or1the rupture oflthe;specimens b cording to theflprocess' of this invention:

that the bond shows a very high resistance to fatigue impact tests. Agood resistance is obs'ervedalso when operating fatigue tests at l00'or120 C.;' the bond itself being highly heat resistant, as already stated.

In order to demonstrate the improvementof our novel rubber-to-metalbonding process, we devised special laboratory tests which are hereafterdescribed for quantitatively evaluating the fmechanical resistance ofthe bonds resulting from our process, in comparison with bonds producedby prior art processes, The results ofthe tests are shown in connectionwith various examples or rubber-to-metal bonds resulting from ou'r novelprocess.

Practical tests carriedouton various types of shock absorbers, elasticwheels, rubber-band tired wheels, rubber lined cylinders and so on arein accordance with the excellent results obtained in the laboratorytests. Y

TEST METHODS Preparation of the test specimens. Twokinds of specimens,which will respectively be called hereinafter of the first type and ofthe second type? were employed in the various tests. g

V The specimens of thefirst type are similar tothe, ASTM specimens (ASTMStandards, 1946, Part 1 I IB Nonmetallic MaterialsrStandard Method orTest for Adhesion of Vulcanized Rubber to Metal, D 429-39). but ofsmaller size, and in addition, the rubberpart is not shaped as acylinder but as a torus of rectangular crosssection, that is, as a ringdefined by two-coaxial cylindrical surfaces, respectively 22 mm. and 10mm. in diameter, and by two planevsurfaces, perpendicular tothe axis ofthe cylindrical surfaces, and 2 mm. apart from each other. Thetwoannular bases of saidrubberring are bonded each to the one face oftwo metal pieces; similarly shaped as cylindrical rings, 10 mm; inheight over their whole exteriors to an'external'4 mmathi'ck metal ringand toahinternal5.8,mrnxthick metal'ringyyvhich are shaped'so'astoallowfthem to beclamped to the specimen is molded into a su'itabletransfer Imold,

Static tensile test.+ The specimens of thefirstftype are subjected totensilestress by meansof. a dynamometer,

havingfa loading, capacity of ;:250 -kg.f andlfitted with a, Y

load-recording; device; the dynamometer being operated 1 during the testso that the moving clamp of th travelsat aispeed of about mm. perminute.

As-stated'forthe A.*S.1T.":M{test, the; values-'ofthe; loadr'equiredfor'the detachment-or ruptureof-thfefrubber; are read and'referrjed'bycalculation to the-CrOSS-:C 'on'ah, arearoftthe' specimen, or eventuallynote-;is ,.-taken that thejspe imen -has not ,beenbroken.

-S tatic shew; tut i-For this test specimenstype arejemployed;-"lihemetal parts ofjthe-specinren beingclamped to' the heads of atorsion dynamometer,} if p em is rotatedfwith.respect to the lotheraround the ax s of symmetry ofthe specimen,,withoutadisplacingr t e; t-S sas t e'sa ax l n l i ac m t; or. the :i upture' ofthe'rubber"occurs. iFromjthelreading of mai imumish a l ad, the periphery ofj'thespecimensfand causing thedetach merit: or the rupture ofjthe rubber, iscalculated: vThe dynamometer is enclosed ina case whose, insidef may be7 o e; f

he s e i the m gma electricallyheated,so" that thertest may becarrie'dout also attemperatures higherthanjroom temperature;

Dynamic'shdr testsQ-These aretwo fatigue tests operated by means ofproper machines,1acting respectively on the specimens. of the two typesand are carried out by men isj rotated with respect, to the other aroundthe axis i of symmetry of the specimen for an angle of 24 alter-' andhaving diameters equal to those of the rubber ring.

The bond surfaces of the metal parts are flat and smootlr j and areparallel and coaxial in the finished' specimen; Each metal piece has agroove on its outer cylindrical surface and is threaded on its innercylindrical surface so as to allow it to be clamped to the testingmachine. .The finished specimen is obtained by inserting a crude rubbercompound ring, shaped'as it will be after vulcanization but slightlythicker, between the two metal pieces, and vulcanizing the assemblyintoa vsectional mold of proper construction in an hydraulicsteam-heated press. The specified diameters provide a cross-sectionalareaofaboiit' 3 cm. square. i

subjecting the specimens to. alternative torsional stresses 4 havingintensities lower than those requiredl'for' causing: a

the immediate detachment orrupture of the rubber parts ;The testemploying the specimens of the firsttype and which willbe hereafterindicatedwith the letter .A,lis' a advisable only for rubber compoundshaving Shore A} 7 hardnesses of about-70'. i i

@In this 'test, ,the one of the metal parts of the specinatively tothe,one direction and to; the opposite one,

under the action of a couple nearly constant -(kg.cm..

1712mm at a'frequency; of- 320 cycles perminute. This test is effectedat room temperature only.

Thefnumber of .cycles"required to cause the detachmentlof the rubberfrom the metal parts or the rupture of. the .rubberfin a rather' widesector is reported.

eIhe' dy'namicfshear test. employing specimens of the second typehereafter indicated with the {letter B, ,is

. operated by :rotating one of the metalpparts with respect.

.to.. the' other aroundthe axis of symmetry of the specimen; t mf t r iopp i rdi ectivn e mi a an les:

. The'torsion angle is selected according tothe hardness or,

The specimens. of the second type have .the rubber part in ring form,defined bytwo cylindrical, circulan'c'oaxial surfaces, respectively 48and 40 mm. in diameter and 4 and 5.8 in height, and by two conicalsurfaces;

rriore exactly, to. thegshejar modulus of the vulcanized rubbercompoundijemployed-lfor thefte'st," so as: to obtain .a maximumshearloadfabout 'the'same for the different rubber compounds The testingmachine is 'enclosedin a' case,', whos'e' inside may be electricallyheatede'so' that' the testmayjbe eifecltedalso at temperatures higherthan rdomtempera'ture'up to C. The number 'of' c'yeles required-to causethe detachmentlofthe rubber'ifrom the" e' machine;- 4

metal parts or the rupture of the rubber in a rather wide sector isreported. t i

' Impact test.For this test specimens of the first type are employed.The specimen being arranged with its symmetry axis in a verticalposition, its upper metal part is clamped to a support fixed atsufiicient height and its lower metal part is attached to the one end ofa metal chain supporting a weight at the other end. Raising the weightat the level of the specimen and allowing it to fall freely, an axialstress is caused. The impact value is calculated by multiplying the fallheight (in. 1.50) by the weight (kg. 3). The number of blows required tocause the detachment of the rubber from the metal parts or the ruptureof the rubber is reported.

Having now described all steps of the process of the present inventionand the various methods for its practical execution, the resultsobtained therefrom are illustrated by the following examplei without thefield of the invention' being thus limited; it being on the contraryextended to all modified embodiments above indicated. When not otherwisespecified, the values reported in the examples indicate parts by weight.

EXAMPLES 1st example-This example refers to the results obtained bysubjecting to the static tensile test a number of specimens manufacturedwith adherence-layers containing components having aflinity for themetals, some sulphurated phenolic compounds, and adhesive solutionscontaining an aldehydimine derived from an aromatic diamine, prepared byone of the following methods.

Mixtures of isomeric monosulphides or disulphides of resorcinol areprepared by reacting in dehydrated ethyl ether respectively sulphurbichloride SClg or sulphur monochloride SzC'lz, and resorcinol in themolecular ratio of 1:2, and then eliminating the solvent as well as thehydrogen chloride formed in the reaction. Reducing the thus obtaineddiresorcinol disulphides by means of granulated metallic zinc anddiluted sulphuric acid, and extracting the aqueous solution by means ofethyl ether, a mixture of isomeric mercaptoresorcinols is obtained.

According to an easier and more economical method, reacting rcsorcinoland sulphur in the ratio of one grammolecule of the former to onegram-atom of the latter at a temperature of 220225 C. for about twohours, a mixture is obtained, which is composed essentially of thercaptoresorcinols and diresorcinol monosulphides and contains alsounaltered resorcinol, diresorcinol disulphides, dimercaptoresorcinolsand resinous resorcinol polysulphides. In this reaction hydrogensulphide is formed.

The raw product resulting from the reaction carried out in the presenceof 1% of liydroquinone on the total weight of reactants will behereafter indicated with the letters "Mixtures richer in resinousresorcinolpolysulphides can be'obtained by reacting resorcinol withlarger amounts of sulphur or of sulphur chlorides, up to thestoichiometric ratio of 1:1.

Other phenolic substances, such as phenol, hydroquinone, and the like,can be reacted with the sulphur chlorides or with sulphur. In order toobtain the reaction of sulphur with phenol a temperature at about 300 C.and pressure are applied. The reaction products of hydroquiuone withsulphur, obtained by melting the react'ants at a temperature of about250 C. are p ractically C a i i s a W ll a the P r QQWPOUHQS which were.7

' 1-2 lated therefrom (phenolic mercaptans, monosulphides, disulphides),can "equally be employed to prepare the adherence-layers. For thispurpose, to the sulphurated phenolic derivative, dissolved in 95 pure ordenaturated ethyl alcohol, a 40% aqueous solution ofhexamethylenetetramine is added and the obtained solution is thendiluted with ethyl alcohol, so as to have a weight rate of 5:2 betweenthe two dissolved substances, with a total solids content of 20%. Theadherence-layer obtained, as above, by mixing the solutions of the R2product and hexamethylenetetramine, with the addition of 3% ofhydroquinone on the total weight of both components, will be hereafterindicated with the letters ERZ. The letters EIRZ will instead indicatethe adherence-layer obtained by employing, in absence of hydroquinone,with hexaniethylenetetramine, the raw product obtained react: ing at220-225" C. 32 parts by weight of sulfur, 9 9 of resorcinol and 11 ofhydroquino'ne. The adherence-layer EIRZ is then coloured by adding to it0.5% of methyl violet on the total solids content.

The monomer difurfurylidene-p-phenylenediamine is prepared by reactingp-phenylenediamine, dissolved or suspended in ethyl alcohol, withfurfural in the molecular ratio of 1:2 and collecting, washing anddrying the prodnot of the reaction. The so obtained raw product will behereafter indicated with the letters PF.

Several rubber stocks are prepared, having the following compositions:

The corresponding adhesive solutions are prepared by dissolving theserubber stocks in benzene, in the weight ratio of 1:5.

In order to prepare the test specimens, an adherencelayer having any ofthe compositions above indicated is lightly brushed on the bond surfacesof the iron parts of specimens of the first type, to obtain a thin film.Two hours later, an adhesive solution having any of the compositionsabove described is lightly brushed on the first deposited layer, toobtain another thin film over it.

' About one hour after, the iron pieces are placed in an oven, preheatedat 160 C. and maintained at this temperature for two hours. 7 I

In order to complete the specimens, pieces of a rubber compound of thefollowing'cornposition which will be named hereafter A50, cut in thestated shape, are asse mjed. t the s? t a ed r n. nie s Rubben (smoked,sheets) 1.00. Zinc oxide l0v Benzothiazilcyclohexylsulphenamide 0.5.Phenylbetanapthylamine 0.8' Phenylalphanaphthylamine 0.2 Stearic acid,4- Channel; black 2-5 Sulphur 2 -5 Because of its content of stearicacid, and ofthekind of accelerator, this rubber compound; is notsuitable'to be attached to brass:plat ed iron. The optimum tensileproperties are obtained by curing this rubber compound for -30 minutes Vv ound s ow he f l o ch nis h a st s is (Schoppers rings) ShoreAhardness Modulus, 300%, kgJcmk 'ljensile strength, kg./cm. 280

Ult mate, e a n. per e 00 at 143"C. Thus cured, the A50, corn Therubber-to-metal bonded specimens'i vulcanized in.

2,71 1,sea;

this manner and subjected to the tensile test, break under differentloads accordingvto the compositions of the ad? herence-l'ayers and theadhesive solutions. When adherence-layers based on puremercaptoresorcinols, diresorcinal disulphides, and the like, areemployed, the breaking loads vary from 63 to 8'3 kg./cm; and when theadherence-layers ERZ and ELRZ arejemployed, the breaking load is, as arule, not inferior and often higher than 83 kg /cmff. I

The rupture normally occurs in the film formed by the adhesivesolution.I

test, the stresses being after, remainingf forlO minutes atthe sametemperatures;

Example 2.'I'hisiexamp1e shows the results of different tests eifectedby using an adhesive solution contain- 6 ing, besides the ingredientswhose use hasjbeen indicatedv in the 1st example, an aldehydiminederived from-an aliphatic diamine,

The monomer difurfurylidenehexamethylenediarnine is prepared by reactingthe 'hexam'ethylenediamine with furtural 'in the molecular'uatio 1:2,ataitemperature"'d not exceeding 50 C;, and. drying the resultingproduct, so as to eliminate the water formed in the reaction. The

raw product of this reactionwill be hereafter indicatedwith the lettersEF.

Three rubber stocks respectively indicated hereafter. by the letters A,B and C,Vare then separately.

prepared, having respectively the following compositions:

Rubber (Smoked sheets) Zine oxide MercaptobenzothiazolePheuyl-beta-naphthylamln Re sorcinol Totals 41. 2

The adhesive solution isprepared by dissolving together 68 parts of therubber stock A, 41.2 of the rubber stock B and 41.7 of the rubber stockC, in 750 parts of smaller :intrinsic resistanceof "the-1 rubberparfof-z'the specimens at such temperatures; Inifact,thisdecreasedresistance is also observed in bonds resulting from other for instance,from the brass-plating process which gives similarly good results whenrubbe r" coin' pounds of the same type,;as-the;M70compound, are

benzene, thus obtaining a weight ratio of about 12501? the total of thethree rubber stocks as compared with the solvent.

On the bonding surfaces of 30 iron parts for themanufacture of specimensof the first type the adherencelayer ERZ, described in the 1st example'is lightly brushed and, an hour after, a thin film ofthe adhesivesolution above described is brushed over it. Half an hour after thissecond application, the metal parts are placed in an oven fitted with anair-circulating device and preheated at 140 C., where they aremaintained for two hours at the said temperature. Theso-treated metal.

pieces'are assembled with a rubber compound having the followingcomposition, which will be hereafter indicated with the letters M70: I I

The optimum tensile properties areobtained by cur-'- ing this rubbercompound for 30 minutes at 143 C.?

Thus cured, the M70 compound shows thefollowing mechanicalcharacteristics:

Shore A hardness Modulus, kg./Cm. Tensile strength, kg./cm. .165Ultimate elongation, per cent 285 The rubber-to-metal bonded specimens;vulcanized under these conditions, are subjected totth e static shear' 1quantity corresponding to one gram-molecule, and then eliminating thejsolient and drying the "product on, a watef-bath in vacuuml j, 7 A1brownbily liquid=is obtained; which" is 1then;di s-' I j sblved in'benzen e and added in an'amount corresponding to 25.2% "of the .rubberbyv veighhftov a benzenicj-solution of theifollowing rubber, stock, soas'to obtain a weight' 'Zin'c oxide u Y na Perm a? 2 others aretested'at'roo'fl temperature after having been subject d o at56 C; e r

Hereafter are listed the .detailed values Sincedetacbment otv therubberfrom the metal parts 3 never occurs, the lower values of thes'pecificlo'adsfin' thef test carried out at 50 C, and 100 Ci.depe'ndion the processes,

employed.

The increase of characteristics of the'rubberzwhich is often'fobs'erved;in

the starting steps of the artificial agingtests, and-=provesi that thebond has remainedunaltered, despite the prolonged standing of thespecimens at .569, C. during the -aging test.

Good results are'also obtained by varying the reso r cinol 7 content inthe adhesivesolution', for instance, by'decreas; ing it from 9% to 3%,orrevenflto 1%, 'on', the rubber? weight; orby substituting-theresorcinol with other phenolic substances, as for instance, the product,gin.

quinone'in amounts from 3 to 12% ;or also byemploying theEF product asthe sole aldehydimine, withoutthe PF the mentioned phenolic com}:

product, together with pounds, or also with phenol in ditferentamountsiExample 3. ThisjeXample relates to an adhesive sold-Q tion containing amixed aldehydimine and illustrates, the .good results obtained ,by itsemployment in 'ditferent tests" 7 7 V Raw methylenefurfurylidene-hexamethylenediamine is prepared by reacting 'a -grammolecule ofhexamet hyhendiamine witha'gram-molecule of furfural,dissolving the product. .thus obtained in ethyl alcohol, adding to thissolution a 38% aqueous solution of'formalclehyde in a ratio of"1:l2tbetweenjithetotal" solids" content and the solvent: e l Rubber smo'k asheets) M t a b nz a ole, Phen et neph i in inci e'asedv until therupture, of aboutione .half of; the rubber parts occurs,kthe detachmentof the rubberfrom ithe metal parts never taking place, Someof thesespecimens. are tested at roomvte'mperature, others a t 50 C. and at 100,Cfrespectively 156385 obtained shear loads calculated foreachspecirneni together withthe corresponding, average values for each jV the specific" load observed in the j speciC- J mens agedat 5 6 g C.,with erespect, to; the imaged speei-I mens,- dependsbntheimprovementinthe mechanical amounts of '5, 10 'or' 15% of' thegrubberpand hydro V 3Anhourlafter havingapplied by brush the adherence layer ERZindicated inthe 1st example, a thin film ofthe j abovezadhesive selutionq is appliedin thesamei way, tov the iron parts for the/manufacture of 8 specimensof the first type and IZspecimens-oE the. second 1 typeglthejadhesiveRutzber compound A60.-

Iensile test, kg.lcm. 838383 Dynamic test B (shear ang1ed=52) At 25,thousands of cycles, 525545-555, average "540 At 100, thousands ofcycles, 465-450-315, average 410 Rubber compound M70:

Tensile test, kgJcm. 718383 Shear dynamic test A, cycle 000-144, 000 IShear dynamic test B (shear At 25 0., thousands of cycles. 750495865,average 700 At 100 0., thousands of cycles, 320'-365365, average "350The rupture of the rubber part occurs in all tests. Example 4.Theadhesive solution described in the foreging examples always containsgreater or smaller amounts of antioxidants. This example refers to theresults obtained with an adhesive solution not containing antioxidantand having, as a sole adhesive agent, the EF product, whose prepartionhas been described in Examplfi 2.

A rubber stock of the following composition is prepared in a two-rollsmill:

Rubber (smoked sheets) 100 Zinc oxide Mercaptobenzothiazole 0.5 HP c 60The adhesive solution, which will be indicated hereafter with theletters GMEF, is then prepared by dissolving 10 parts by weight of thisrubber stock in 135 parts by weight of refined benzene. In all cases theadherence-layer ERZ, described in the 1st example, is used. The rubbercompounds M70 and A50, whose compositions have already been given, aswell as the two followlng ones, are employed:

Rubber compound "E40 E65 Rubber (Smoked sheets) 100- 100 Zinc oxide c 1010 Benzothiazyldinitrophenylsulphidc 0. 75 0. 75 Diphenylguanidine 0. 50O. 50 Phenylbetanaphthylamine, 0. 80 0. 80 Phenylalphanaphthylamine 0.0. 20 Stearic acid 0. 50 0. 50 FF Black 50 Sulphur 3 3 The E40 and E65rubber compounds give particularly poor results on brass-plated iron.times for them are respectively 20 and minutes at 143' C. Vulcanizedunder these conditions, these two rubber compounds have the followingmechanical characteristics:

Rubber c0tnpound i E40 E6 Shore A hardness 40 05 Modulus 300%, kg./cm 130 190 Tensile strength, kg./cn1? 200 110 Ultimate elongation, percent500 375 The adherence-layer and, an hour later, the adhesive solutionare applied, as a rule, in this example, by brushing lightly on themetal parts, so as to obtain thin films; the resinification alwaysoccurs about an. hour after the second brushing and the vulcanization iscarried out under the conditions already stated for each rubbercompound.

The metal to which the bond has been efiected, the quality of the rubbercompound, and the resinification conditions, when differing from thestandard (2 hours at- The optimum curing 140 C.), as well as thetemperature of the shear namic test B, are specified in every instance.

The specimens assembled with iron parts and with all four rubbercompounds give, at tensile test, detachmerit loads equal to or higherthan 83 log/cm For comparison, the direct bond of the rubber compoundM70 to brass-platediron has, been efiected with the same specimens; thusgiving an average detachment load of about kg./cm. i

In a series of 25 shear dynamic tests A, etfected on specimens havingiron parts assembled to the rubber compound M70, and performed indifierent periods of time, durations corresponding to from 80,000 to210,000 cycles, with an average of 142,000 cycles, were obtained. Therupture of the rubber, instead of its detachment, always occurred. Bytesting, under the samev conditions, the specimens assembled with theE65 rubber compound, the following results have been obtained:

Thousands of cycles, 139-176173-154, average 160 Specimens of the firsttype, prepared by directly assembling the rubber compound M to thebrass-plated iron parts, have lasted for a period of time correspondingto about 100,000 cycles. 7

In a series of shear dynamic tests B, on specimens having iron partsassembled to the one or to the other of the four rubber compounds,wherein the heat-treatment in circulating air of the solutioned metalparts has been made, as hereafter indicated, for difierent periods oftime at difierent temperatures, said tests being effected under thehardest conditions, that is at C. and C., the following results wereobtained:

Resinification time Thousands of cycles Cycles average Rubber compoundA50 Test tempera- (shcar angle =|=52): ture 100 C.

2 hours at 146160133l91-171 160,000 1 hour at 220-280-270 257, 000 20wins. at l70200l30... 167, 000 10 mins. at 120-310-140 190, 000

Test is mpera- V ture 120 C.

2 hours at; 140 C 92-85-779283 86, 000 Rubber compound M70 Test tompera- (shear angle 5110): time 100 C.

2 hours at 140 263590530-41743l 446, 000 1 l'lou-rrat 150; 480-520- 580527,000 20 mins. at 160 480410-5S0 401), 000 10 mins. at 170 571)440580533, 000

Test tem eratil-T8190 CZ, 2 hours at;- 140 240-150290-260-310., 250, 000Rubber, compound E40 Test tern era- (shear. angle =|=52) ture 100 C.

2 hours at 140; 123284.-2402-12l'42 200, 000- Rnhber compound E65 (shearangle 140): 1 i

2 hours at; 140 280-46( 430-400530L. 120, 000

Specimens of the firsttype, having: iron parts assembled to the E65rubbercompound, were subjected toan arti ficial aging test forO-3.7-l421 days in an oven. at

78 C. At the. end of. the. respective. aging. periods, the

specimensiwere subjected either to static tensile tests, or todynamicshear tests A, and the following results: were observed:

S Tensile sh A 1 pecu'nens test, ear test cyc es uuuged,.kg. /cmfl'83-83 83' 240,000-1-76,000-l54;000 aged 3 days at 78 C 8383, 230,000134; 000' aged 7 days'at'78 C' 8381 230, 000197, 000 ged 14 days at78 (3.. ,83-.83 230, 000-154, 000 aged 21 days at 78 C 62-74 69,COW-154,000

have been subjected alsoto}v Thefadhesive solution-being also air-dried,the metal parts I are'submitted to-ratwo-hour heat-treatment at, 140 Cinan oven-in which air. is circulating. .The specimens are 7 obtained byassembling the said solutioned f and heattreated metal partswiththe'rubber compoundM70 and by. vulcanizing. the thusobtfainedassemblies for 30-min V V utes at,143. C; Said specimens,"whensubmittedeither V to the tensile tests, or to thedynamic shear test A, gaveobtained assemblies were then vulcanized for'30 minutes I at 143 C. Inthe following table the numbers of blows required to cause the ruptureof the specimens, areshown:

average 9.

Rubber compound A50 Rubber compound M70 In the specimens assembled withthe A50 rubbercompound, rupture occurred in the film formed from theadhesive solution, while in those assembled with the M70 rubber compoundthe rubber part'was broken.

Comparison specimens, prepared by directly vulcanizing the rubbercompound M70 on brass plated iron parts,

broke under the same conditions, afteronly one or two blows. g

Static tensile tests and dynamic shear tests A"were also performed onspecimens prepared by paint-brushing the adherence-layer ERZ and theadhesive solution GMEF on previously sand-blasted parts of non-ferrousmetals. (or parts of iron clad withother metals, such as lead),by;subjecting the said solutioned'metal parts to a two-hour heat treatmentat 140 C., assembling these-treated and solutioned metal parts to therubber compound M70, and

vulcanizing the assemblies'for30 minutes at'143" C. The 85 followingresults were obtained for each metal:

V V I I i 7 Shear Metal g .Test A,

cycles Aluminium, kg./cm. .Q S3-83 110, 000 Zinc, kgJcmfi 83-83 t 102,000 Lead (lead clad iron), kg./cm. 83-83 88, 0 Copper, kg./cm. 64 76154, 000 Brass, kgJern. 73-83 134, 000 Stainless steel 18/8, kgJem.64-76 50,000

The rupture of the rubber was noted for the-highest values, thedetachment occurring otherwise than in the w compounds', arefined-product' is; obtained, consisting'ofa V 'diresorcinol.sulphoxides, withsmall amounts of thejprod-Q tory results have also .been obtained onspecimens pro vided with nickel-plated copper parts. When brass parts iare involved, this process shows, in comparison withthe direct bond, theadvantages not being limited by the conipositions of the rubber compoundand of the brass, and yet obtaining safer and better results.

Similarly good results are obtained by employing, in the preparation ofthe adhesive solution, instead of the EF product, thedi-furfurylidene-di beta-aminoethyl sulphide, which is an aldehydiminederived from a linear aliphatic diamine including in its polymethylenicchain'an heteroatom.

Example 5 .This example shows the results obtained when employingan'adherence-Iayer containing, as a component having afiinity formetals, 1.3-dimercaptobenzene, that is, a product not containingphenolichydroxyles, but only two sulphydrilic groups in a benzenicnucleus. The adherence-layer is prepared by dissolving 10 parts of 1.3-dimercaptobenzene and 0.4 part ofhydroq'uinone, as an antioxidant, indenatured 95 ethyl alcohol, by adding 4 parts of hexamethylenetetramineas an aqueous 40% solution, and adding ethyl alcohol, so as to reducethe total solids content to 20% by weight. This adherence-layer isbrushed on the metal parts of specimens of the first type, made of, orplated or clad with, the metals hereafter indicated. Just after thefirst layer is air-dried, the adhesive solution GMEF, as described inthe Example 4, but .diluted in an equal part by weight of benzene, issprayed.

ucts' hereafter described.

4 the'following results:

cm. 7 Stainless steel 18/8, kgJemL ,The' rupture ofthjflibberwasfobserved v specimens provided' with iron, brass and lead cladironparts. *The tearing of the formed from the adhesive jsolution'ioccurred with the aluminium, "zinc, c'oppe'rer tinned parts]The detachment from the 'metalon' relative" ly; extensiveareas,toccurred-?in the peeimens' assembled V ,withpickelplated copper,chrome' -plated copper or stain-' less steel parts. T

Exdmp le' 6; Thisfexampleshows the-results. btained m l y n h en e-lyerscontaining as"compo nentsj having aflinit y for metals; two reactionproducts of resorcinol with thionyl chloride, preparedin-the presence ofanhydrous i aluminiumchloride. c

Byreacting resorcinol with'thionylchlonde(molecular ratio, 112)dissolved in a mixture of dehydrated ethyl ether: and carbon disulphide,in the presence ofasmall quantity-- of dehydrated' aluminium chloride,and. eliminating from" the rawreact'ion product the solvents and the?aluminium.

By reacting'resorcinol, thionylchloride andpdehydrated;

. aluminium chloride in the ,same.solvents,;themolecular" p s I stanceis obtained, which, has the behaviour and 'composi film formed from theadhesive solution. Some sat1sfaction' ofa.resorcinol-sulphoniumchloride.

Two adherence-layers, which shallbe named ,Resorcinol sulphoxideHexa?"and Resorcinol sulphoniumchltF ride-Hexa were prepared by:dissolving theone'or. the r other, of the .two aforesaid resorcinolderivatives inethyl alcohol, and mixing the solution with a"40%"aqueousso of 5 liby weight inboth' when submitted either tothe tensiletest,

lution of:hexamethylenetetramine,.the solids ratiobeing cohol,'soas-tohave-atotalsolids content of 17%. v Specimens of the 'firsti type.were prepared with these adherence-layers, employingthe GMEFadhesivesolution and. the M rubber-compounmand metal parts; made of,

' orplated, or clad with, different metals, according to the methodindicated, in the Example 5 Said-specimens,

shear-test A,- gave thefol-lowin'g results:

j asesjand dilutingiwith'ethyl al- I or m h d nami The rupture of therubber, or the tearing of the film formed from the adhesive solutionwere observed in the specimens provided with iron, copper, brass, orstainless steel: parts. With the other metal parts, some more or lessextensive detachments were observed near the metal.

Adherence-layer Resorcinol sulphonium chloride-Hexa In all these tests,the rupture of the rubber occurred. Example 7.This example shows theresults obtained when employing adherence-layers containing, as compo-.

nents having aifinity for metals, the hereafter indicated phenolicsubstances. Said adherence-layers were prepared by mixing an alcoholic,or alcoholic-acetonic, solution of the phenolic substance, according toits solubility, with'a 40% aqueous solution of hexamethylenetetramine,so as to obtain the solids ratio by weight for every substanceindicated, and a total solids content ranging from 6 to 20%. Accordingto its concentration, the adherencelayer is applied by spraying or bybrushing on iron parts. Some adherence-layers were applied also toaluminium parts. The adhesive solution GMEF and the rubber compound M70were successively applied, according to the method indicated in theExample 5.

The specimens provided with iron parts gave the following results:

Specimens provided also with iron parts and made identifically, butemploying adherence-layers prepared by using, instead of a singlephenolic substance, a mixture of pheno1..withresorcinol, or with the RZproduct, in equal parts by weight, the ratio of the total of bothphenolic components, with hexarnethylenetetramine being always of 5:12,.gave in. the tensile tests, detachment loads of 5953 and 76-70 kg/cm.respectively.

The specimens provided with aluminium parts gave the followingresults:

Solids tensile shear Phenolic substance ratio test, test A, kg./cm 2cycles resorcinol 5: 2 70-72 102, 000 echlororesorcinol 5-. 2 i353 58,000 phlrogllieinol 5:2 40-42 58, 000 p,p' -dlhyd.r0xydipbenylsu1phone 52 3937 45, 000' Example 8'.This example shows the results obtained whenemploying an adhesive solution containing, besides the natural rubber, arather high amount of reclaimed rubber. A rubber stock of the followingcomposition was i used:

Rubber (smoked sheets); 100 Tire tread reclaim 200 Zinc oiride 40Mercaptobenzothiazole 0.5

The reclaimed rubber indicated above is of the type obtained byheat-softening tire tread scraps mixed with 10% coal tar oil. To theabove rubber stock dissolved in benzene, the product EF, also dissolvedin benzene, is-

added, in an amount of 180% of the rubber by weight (equivalent to on:the total content of rubber and reclaimed rubber). The total weight ofbenzene is adjusted so as to obtain a ratio of 1:15 by weight betweenthe total solids content and the solvent. The adherencelayer ERZ and theadhesive solution, as above indicated,

are brushed at a convenient time interval on the iron parts of thespecimens of the first type and, after evaporating the solvent, thesolutioned iron parts are subjected to a;

two-hour heat-treatment at 140 C. The rubber compounds A50 and M arerespectively assembled with the solutione'd and heat-treated metalparts, and the speci mens thus obtained are vulcanized for 30 minutes at143 C. The following results were obtained with these specimens in thetest hereafter indicated:

Rubber compound A50, tensile test, kg./cm. 67. 53 Rubber compound M70;tensile test, kg./cm. 8383 Shear test A, cycles 115,000-420,000

The tearing of the film formed from the adhesive solution occurred inthe specimens assembled with the rubber compound A50, and the rupture ofthe rubber in those assembled with the M70 rubber compound.

Example 9.--This example shows the results obtained when using acompound based on a rubbery butadieneac'rylonitrile copolymer. Acompound of the following composition was employed:

Indicates a synthetic rubber consisting of a butadie'neacrylonitrileccpolymer (containing about 38 percent comb11186 acrylonitrzle}manufactured by Copolym'er Corporation, Sarnia,Canada-. h

Optimum tensile properties were obtained by curing this compound for 3-0minutes at 143 C. Thus cured, it

showed the following mechanical characteristics:

Shore A hardness 58 Modulus, 300%, kg;/cm'. Tensile strength, kg./cm-.Ultimate elongation, per cent 400 To prepare the adhesive solution, arubber stock having the following com-position was employed:

(Semi-reinforcing furnace) black 40 *Indicates a. synthetic rubberconsisting of a butadieueacrylonitri-le cop'olymer (containing about 38percent ep nblne'd acrylomtrile) manufactured by Copolymer Corporation,Sarnia, Canada.

The pepti'zin'g agent here employed was a mixture of equal parts oit-richlorothiophenol and para-{fin wax.

in order to prepare the adhesive solution, the last described rubberstockwas dissolved in benzene, and to the thus-obtained solution, the EFproduct, also dissolved in benzene, was added in an amount correspondingto 60% by weight on the rubber. The amount of benzene was adjusted so asto obtain a ratio of 1:13 by weight between the total solids content andthe solvent.

The adherence-layer ERZ and the above adhesive solution were applied tothe iron parts of the specimens of the first type, heat-treated,assembled with the rubber compound above described, and' the assembliesvulcanized, as

' 21 7 indicated in the preceding example,;temperatures and times of theheat-treatments being as shown therein. With these specimens, thefollowing results were obtained:

Tensile test, kg./cm. 83-83 Shear test A, cycles 88,000

In every case the rupture of the rubber part occurred. Example 10.Thisexample shows the results obtained when using a compound based on arubbery chlorobutadiene polymer. A compound of the following compositionwas employed: a i

"*Five specimens of cess ively'. with the adhesive solution GMEF, andsub mitted to atwo" ho r iratment ai 1 93 inioven 7; h. e m e Vulcanized5 at 143 0., were then cooled unde p je w in which air is circulating,

lating water in the press. Th'ese specimensv showed thefollowingresults: e

' In all cases the rupture oflthe compound occurred near j the filmformed from the adhesive solutiong- 1 Optimum tensile properties wereobtained by. curing this compound at 143 C. Thus cured, it showed thefollowing mechanical characteristics: a a

Shore A hardness Modulus, 200%, kg./cm. Tensile strength The adhesivesolution wasprepared by dissolving someneoprene GN-A in benzene, addingto this solution the Ultimate elongation, per cent 210 :30

EP product, also dissolved in benzene, in an amount of V 60% by weighton the rubber and diluting the solution with the same solvent, so as tohave a total ratio of 1:15 by weight between the total solids contentand the solvent. The adherence-layer ERZ and the said solution werebrushed, at a convenient time interval, on,the iron parts of thespecimens of the first type, heat-treated,

assembled with the rubber compound above described, and the assembliesvulcanized, as indicated, in the preof the heatceding example,temperatures and times treatments being as therein. With these specimensthe following results were obtained:

Tensile test, kg./cm. 67-58-67 Shear test A, cycles from the adhesivesolution,

with partial rupture of the rubber.

Example 1].This example shows .the results obtained from the classconsisting: of diffirfur'ylidenahexamethybI when employing a compoundbased on an ethylene tetrasulphide polymer. A compound having thefollowing composition was employed: e

Thiokol A 100 Rubber (smoked sheets) 7 Zinc oxide 7 10Tetramethylthiouram disulphide 0.15 Diphenylguanidinepun 0.30 Stearicacid I '5 Carbon hlaclr 25 Optimum tensile properties were obtained bycuring this compound 20' at 143 C. Thus cured, it showed the followingmechanical characteristics: a

Shore A hardness g 75 Tensile strength, kgJcm.

Ultimate elongation, per cent 300 96,000 The detachment always occurredin the film formed ,1 While we haveshown and described the preferredem-I *bodiments of our invention, .we do. not'limit ourselves'to thedetails'of processes orconstructionsdisclosed-by way as-these'may bechanged, and modified hy those skilledin thefart. without departingfromthe spirit of ourinve'ntion or exceeding the scope of the ap ofillustration,

pended claims. a

. We claim: Li-A process for perature of from 110 Cfto 0.;

molecular weight, 'of which at least one has affinity for metals; saidadhesive solutioncontaining atleast one rub ber, capable of bonding byvulcanization 'with said rubber compound, and at least one nitrogenoussubstance capable of reacting with said substances having afiinity formetal's; V to form an insoluble, non-melting and metalradhe ringresin,during said first heat treatment; saidjnitrog'e'nous substancesbeing N-substituted aldehydimines having .a f- I plurality ofazomethinic groups corresponding to the genand a monovalent organicradical.

2. AEproces's according to claim 1, wherein one'of Y saidN substitutedaldehydiminesjs monomeric difur- ,furylidenehexamethylenediamine.

3. A;process according to claim 1,;wherein said N-substituted'aldehydimines are monomeric and are selected enediaminqN-methylene-N furfurylidene-hexamethylfurfurylidene-di-beta-aminoethylsulphide. I

i I References Cited 'in of this patent UNITED STATES PATENTS thelirsttype we re. prepared i "assembling'the above rubber compound withi'ronparts i i a previously'treated with the adherence-layer ERZandsucbonding nietal and'me'tal 'alloy's to a vulcanizable rubbercompound characterized by;-s'uca cessively applying to clean bondingsurfaces of said metal. I 1 parts an adherence layer and .anadhesiv esolution, heat treating at a temperature of from 100 C.- toff C the sotreated metal parts in the presence of air,;applyin'g: the

said rubber compound to the so treated surfaces of said) 5 metal parts,and subjecting'said assembledimetal and rubber components to avulcanizing heat treatment atfa'tema.

n 7 sa'idiadherence' layer, containing no rubber and. only subs'tancesoflow} V "where [i {is an integer; higher than 1, R118 anoi'ganicradicalof r z.valen cy,*and' T Rrepresents a radical consistingof one atom'of hydrogen"

1. A PROCESS FOR BONDING METAL AND METAL ALLOYS TO A VULCANIZABLE RUBBERCOMPOUND CHARACTERIZED BY SECCESSIVELY APPLYING TO CLEAN BONDINGSURFACES OF SAID METAL PARTS AN ADHERENCE LAYER AND AN ADHESIVESOLUTION, HEAT TREATING AT A TEMPERATURE OF FROM 100* C. TO 180* C. THESO TREATED METAL PARTS IN THE PRESENCE OF AIR, APPLYING THE SAID RUBBERCOMPOUND TO THE SO TREATED SURFACES OF SAID METAL PARTS, AND SUBJECTINGSAID ASSEMBLED METAL AND RUBBER COMPONENTS TO A VULCANIZING HEATTREATMENT AT A TEMPERATURE OF FROM 110* C. TO 170* C.; SAID ADHERENCELAYER CONTAINING NO RUBBER AND ONLY SUBSTANCES OF LOW MOLECULAR WEIGHT,OF WHICH AT LEAST ONE HAS AFFINITY FOR METALS; SAID ADHESIVE SOLUTIONCONTAINING AT LEAST ONE RUBBER, CAPABLE OF BONDING BY VULCANIZATION WITHSAID RUBBER COMPOUND, AND AT LEAST ONE NITROGENOUS SUBSTANCE CAPABLE OFREACTING WITH SAID SUBSTANCES HAVING AFFINITY FOR METALS, TO FORM ANINSOLUBLE, NON-MELTING AND METAL-ADHERING RESIN, DURING SAID FIRST HEATTREATMENT; SAID NITROGENOUS SUBSTANCES BEING N-SUBSTITUTED ALDEHYDIMINESHAVING A PLURALITY OF AZOMETHINIC GROUPS CORRESPONDING TO THE GENERALFORMULAR R(-N=CH-R'')N, WHERE N IS AN INTEGER HIGHER THAN 1, R IS ANORGANIC RADICAL OF N VALENCY, AND R'' REPRESENTS A RADICAL CONSISTING OFONE ATOM OF HYDROGEN AND A MONOVALENT ORGANIC RADICAL.